System of neutralization



July 7, 1931. H. F. ELLIOTT 1,813,036

SYSTEM OF NEUTRALIZATION Filed March 11, 1927 PIE B IN V EN TOR ar'o/dF. E///b ff HIS ATTORNEY Patented July 7, 1931 UNITED STATES PATENTOFFICE HAROLD F. ELLIOTT, OF PALO ALTO, CALIFORNIA, ASSIGNOR, BY DIRECTAND MESNE ASSIGNMENTS, TO VICTOR TALKING MACHINE COMPANY, OF CAMDEN, NEWJERSEY,

A CORPORATION OF NEW JERSEY SYSTEM OF NEUTRALIZATION Application filedMarch 11, 1927. Serial No. 174,475.

- This invention relates to amplifier systems, and especially those thatare adapted for the amplification of minute electrical impulses of highfrequency.

Such systems are in extensive use for example in connection with radioreceiving systems, for amplifying, at radio frequency, the receivedsignaling impulses. For each stage of amplification, use is made ofelectronic emission devices, usually termed audions, each comprising anevacuated vessel having a number of electrodes (usually three) sealedtherein. One of the electrodes (the cathode) is used to throw offelectrons, and is usually in the form of a heated filament in order tosecure this function. Another electrode, usually termed the plate oranode, receives the electron discharge which is attracted to it bymaking its potential positive with respect to the cathode. The spacecurrent thus formed has been found to be sensitive to potentialconditions in the space traversed thereby. This phenomenon is utilizedby providing a control electrode, such as a grid, that influences thepotential of a point in the space. The grid and filament are connectedso that their potential difference is a function of the receivedimpulses; and as this difference varies, the space current iscorrespondingly varied, the variations being relatively much greaterthan the potential variations between the grid and filament. A circuitconnecting the plate and filament permits Variations in this spacecurrent to be used as amplified impulses that can be impressed on asucceeding stage.

This amplifying function is now well understood, and requires no furtherelucidation. The important feature that is to be noted is the fact thatsuch amplifier stages, when used for high frequency currents, as radiofrequency, and especially if several are placed in.

cascade, have a tendency to instability, and to support oscillationsthat disturb the operation and may destroy the clarity of the signals.This effect is due to the reaction of one part of the system uponanother, either capacitively or inductively. One especlally annoyingreaction is that due to the capacity between the grid and the plate,whereby a feed back is obtained from the output circuit to the input.Furthermore, there may be an undesirable reaction between one stage andthe next preceding one through the interstage coupling.

It is one of the objects of my invention to avoid these undesirableeffects.

Although schemes for neutralization have been heretofore proposed, I aimto provide a. novel and better system for accomplishing that result.

It is another object of my invention to provide an improvedinstrumentality whereby the neutralization is accurately and easilyeffected.

My invention possesses many other advantages, and has other objectswhich may be made more easily apparent from a consideration of oneembodiment of my invention. For this purpose I have shown a form in thedrawings accompanying and forming part of the present specification. Ishall now proceed to describe this form in detail, which illustrates thegeneral principles of my invention; but it is to be understood that thisdetailed description is not to be taken in a limiting sense, since thescope of my invention is best defined by the appended claims.

Referring to the drawings Figure 1 is a wiring diagram of one completestage of amplification utilizing my invention, shown as applied to aradio receiving system with one or more stages of radio frequencyamplification;

Fig. 2 is a view, partly in section, of a radio frequency transformer bythe aid of which my invention may be practiced; and

Fig. 3 is an enlarged detail thereof.

In Fig. 1 I show a conventional form of pick-up circuit, such as theantenna 11, loading coil 12, and ground 13. This circuit may beinductively coupled to a tunable circuit 14, including the coil 15coupled to coil 12, and a variable condenser 16. An a-udion amplifier 17is provided, having an electron emitting electrode 18 in the form of afilament heated from the battery 19. There is also provided a. plate oranode 20, and a control electrode or grid 21. The grid and filament areconnected respectively to opposite terminals of condenser 16, wherebyradio frequency impulses received by circuit 14 serve to createcorresponding variations in potential difference between the grid andfilament. One sideof the filament can be grounded, as shown at 22. I Theoutput circuit, carrying the amplified impulses, extends from plate 20,through a winding 23, B battery 24c, back to the filament 18. Abypasscondenser 25 for the radio frequency currents can lbeprovided around thebattery 24, whereby only the steady plate current passes through thebattery, the impulses passing "through the condenser.

' A succeeding stage of amplification,"utilizing, audion 26, can becoupled to the first stage, as by the aid of a secondary Winding27,1forming one-element of the tunable Cir-- cuit 28. 'This'circuit isin-turnconnected to the input electrodes of the audion 26, and the otherconnections of 'this second stage can be made entirely similarto thoseof the first stage theradio frequency stagescan finally lead to adetector andaudio frequency amplifier system 29, which supplies audiofrequency currents to a translating device, such as phones 30. .Suchcascade connect-ions between the stages of amplifiers and the detectorare now well knofWm-and needs no further elucidation.

Dueto the use ofradio frequencies, parasitic capacityeffects exist inthe audions, such as indicated by capacity 31 betweenthe grid 21 andplate 20, I shall now describehow the deleterious effects of suchcapacities can be overcome. A coil32', closely coupled to primary 23 and"having identical characteristics as coil 23, is connected at 'oneend tothat'end'of coil 23 which is nearest battery 24. Its'other .endconnectsto a small condenser 33, whichis in'turn connected to grid 21..The capacity of-condenser33 is "made substantially equal to theparasitic capacit 31. v

The capacities 31,33 and coils 32, 23 form the four arms of asymmetrical bridge; and coil'32 is arranged to oppose the effect of coil23. Potentials induced in coil 27 'due to currents passing thru coil23'from the para? sitic coupling 31 are opposed and neutralized by thesubstantially equal and opposite potentials induced therein duetocur'rentspass-v ing thrucoil 32 via condenser 33. Thus no current canbe induced in secondary 27 from the preceding stage other than thatwhich is due to the variations in the electron stream in audion 17. Ametal shield 34 is also pref erably provided to prevent either inductiveor capacitive coupling between the stages;

Now let us consider theetlect of the cur,- rent circulating in circuit28, upon the pre ceding stage. This can be shown to be neutralized. Coil27 induces, in primary coil 23, and neutralizing coil 32, equal and inphase E. M. ,F.s that are additive and that fixedin the tube,- saidmemberhavingapetancesi32 and 23,..and -'the equality of the potentialsinduced in .32 (and 23 "by. currents in 27. Point 35 is connected to oneinput electrode-'21; and the other electrode 18 is connected to point 36through a by-pass con- 'denser'25, of such 'large value as to bepractically a short circuit for radio frequency currents. Due to groundconnection 22, the points- 3 5 and 3 36 are at substantially groundpotential as regards currents induced from coil 27.

In order to ensure accuracyof-neutraliza- '7 tion, coils-32, 23 and 27 vmust be closely -ooupled and compactly arranged. I I show in Figs; 2and3:how these results can be very simply provided.

I -util'izea tube 37 of insulation swchas bakelite, over which I windthe secondary 27. In one instance the tube was aboutl fl diameter and 1%long, the secondary being fine insulated Wireof about 85- turns. Disposed in I the tube 37 is a disc-likemember 38 ofinsulation in whichthere are-two narrow grooves 39 and40,-'of about the proportions shown.In one of the grooves-,suchasAO, I windgprimary 2'3 (shown-in section),in one instance, with about 25 turns. In'the other groove 39 is thesimilarly wound, neutralizing vcoil'32. Both these coils-are "placedvery close together, so that there istight coupling betweenttheimas Wellas with secondary 27. Lead 41 is indicated as extending tothe commonjunction. point of coils 32land23; and

to facilitate this, apertures 42, 43 and 44 are 7 provided in-member 38.The free ends of coils 32 and 23iare-connected to leads-45nd 46 alsoextending through similar apertures 47, 4s and 49. I

Preferably, member 38 is made from a single piece of such material asba-keliite althoughitis possibleto buil'ditup fromseve eral pieces.Also, it can be fastened into tubei37 near oneendjthereof-iinorder:tomake it easily accessible. The factthat'se'condary 27 encompasses the other coils closely helps materiallyin securing the beneficial stabiliih ing results. 7

'I claim:

1. In combination, an insulation tube, o, coil woundon-the tube, adisc-like member ripheral slot therein that is closed tube, and a coilin said slot. I

Apparatus oft-he class described includin g three coils having coaxialand closely adby l the jacent windings, one of said coils enclosing l5;-

Lei

the other two coils and said other two coils being axially spaced withinthe outer coil.

3. Apparatus of the class described including a. plurality of coilshaving coaxial and closely adjacent windings, two of said coils beingconnected in series and having a common intermediate terminal andanother of said coils enclosing both of said two coils.

4. Apparatus of the class described including a tubular supportingelement, a coil wound on the exterior thereof, and a pair of axiallyspaced coils supported within said element and surrounded by saidexterior coil.

5. Apparatus of the class described including a plurality of coilshaving coaxial and closely adjacent windings, a tubular sup portingelement for one of said coils, and a disk-like supporting elementmounted within the tubular element and supporting a plurality of saidcoils in axially spaced relation to one another.

6. Apparatus of the class described inclu ing an insulation tube, a coilwound thereon, and a disk of insulating material mounted Within saidtube and having a plurality of coils wound on the periphery thereof.

7. Apparatus of the class described including a tubular support, a coilwound thereon, a disk mounted Within said tube and having a pair ofclosely adjacent grooves in the periphery thereof, and a pair of coilsone in each of said grooves.

8. Apparatus of the class described including a tubular support, a coilwound thereon,

3 a disk mounted within said tube and having a pair of grooves in theperiphery thereof, a pair of coils one in each of said grooves, saidpair of coils being connected in series and having a common intermediateterminal, and all of said coils being closely adjacent to provide tightcoupling therebetween.

9. Apparatus of the class described including a plurality of coilshaving coaxial and closely adjacent windings, one of said coils beingtubularly wound and the other two coils being of flatannular form andbeing positioned closely adjacent one another within said tubularlywound coil.

In testimony whereof I have hereunto set my hand.

